For military purposes, there has been developed various laser technologies which intercepts a long-range mortar, a missile or the like from the air or ground. Recently, as a part of the MD (missile defense), USA has carried-out a successful experiment with the air borne laser test bed for intercepting a liquid-fueled ballistic missile launched from the ground.
In a conventional apparatus for intercepting a missile or the like using laser, firstly, it was necessary to irradiate a tracking laser beam to the missile and to analyze velocity and height of the missile and atmospheric status with a computer and then irradiate an intercepting laser beam, thereby intercepting the missile.
One of problems in the conventional intercepting apparatus is to form the high energy laser beam which is mainly formed by amplifying and combining multiple laser beams. A technical problem in combining the laser beams is to overcome wave-front distortion of each laser beam. To this end, there has been proposed a new technique using an adaptive optics and a phase conjugate mirror.
Another problem in the intercepting apparatus using the high energy laser beam is to irradiate the high energy laser beam to an exact position so as to intercept a target. At this time, one of important factors is an atmospheric disturbance between the target and the intercepting apparatus.
Since the atmospheric disturbance functions as an optical dispersive medium, the laser beam is distorted and refracted through the atmospheric disturbance, and thus it is not possible to exactly intercept the target. That is, the laser beam may be irradiated to a wrong position which is apart from a target. And also the laser beam wave-front is to be distorted by the atmospheric disturbance and the intensity distribution becomes distributed widely at the target so that the damage on the target becomes very weak. To solve the problems, the adaptive optics is generally used to compensate the wave-front distortion due to the atmospheric disturbance. In the adaptive optics, the wave-front distortion is previously measured by a wave-front sensor so as to actively control a deformable mirror having a piezoelectric actuator, thereby compensating the wave-front.
As described above, since the adaptive optics also compensates the wave-front distortion caused by large amount of heat of a laser gain medium in the laser amplifying process, it is also widely used in a amplifying system for a high energy laser beam.
However, the adaptive optics has some disadvantages in that its response speed is restricted by the piezoelectric actuator, its manufacturing cost is too high, it is too bulky and heavy, and its operation is very complicated. Furthermore, in order to measure and compensate the wave-front distortion using the wave-front sensor and the deformable mirror, the adaptive optics should have a very complicated construction even though it gives incomplete wave front compensation.
In other words, the conventional intercepting apparatus, which has the adaptive optics so as to solve the problem of failing the target interception due to the wave-front distortion and the light refraction when irradiating the high energy laser beam to the target, has a high manufacturing cost and a complicated driving mechanism. Thus, it is difficult to stabilize the apparatus and the response speed is restricted.